Negative resistance crystal controlled oscillator



E. L. KOCH Feb. 4, 1936.

NEGATIVE RESISTANCE CRYSTAL CONTROLLED OSCILLATOR Filed April 16, 1932 aINVENTOR L J'arZL .ifoc/z mATToRNEY Patented Feb. 4, 1936 UNITED STATESNEGATIVE RESISTANCE CRYSTAL CONTROLLED OSCILLATOR Earl L. Koch, Chicago,111., assignor, by mesne assignments, to Earl L. Koch HoldingCorporation, New York, N. Y., a corporation of New York ApplicationApril 16, 1932, SerialNo. 605,643

3 Claims. (01. 250-36) This invention relates to improvements innegative resistance crystal controlled oscillators as commonly used inconnection with radio systems for various purposes and more particularlyrelates to the application of crystal control to any form of negativeresistance device.

Existing types of crystal controlled oscillators are of the regenerativetype requiring a circuit containing inductance and capacity tuned toapproximately the natural period of the crystal.

In the present invention the generated frequency of the crystal ispractically entirely dependent on its inherent natural mechanical periodand is not subject to changes in the tuned circuit containing inductanceand capacity.

As the application of piezo electric crystals to known arrangements ofcontrol is well known, it will not be described in detail. Generalarrangements usually consist of an ordinary three-element tube havingthe crystal connected across its input and having a tuned tank circuitconnected to its output or plate circuit; Such arrangements depend uponthe inherent grid to plate capacity of the tube for obtaining feedback.

The present invention consists of the use of a piezo electric crystal inconnection with a negative resistance device such as an arc, dynatron ora negative resistance tube such as that shown in the pending applicationSerial No. 537,539 filed May 15, 1931. The crystal is used in such amanner that the usual tuned circuit containing inductance and capacityis dispensed with entirely permitting the crystal to actually oscillateat its natural frequency and almost entirely free from externalinfluence. The result is that the crystal is more completely the singlecontrolling fac-- tor in the determination of oscillation frequency thanhas hitherto been the case.

Two embodiments of the invention will be described in the followingspecification in which:

Figure 1 is a circuit diagram illustrating the invention employing anare or gas-filled two-element tube having a negative characteristic, and

Figure 2 is a circuit diagram showing a dynatron as the negativeresistance device.

Referring to Figure 1, I is a suitable source of energy for the are H(which may be a twoelement gas filled tube).

The numeral i2 denotes a radio frequency choke coil, it a blockingcondenser to keep the voltage of It off the crystal electrode I l. Thenumeral l5 denotes the crystal proper and I6 is the remaining electrodethereof which is connected to the minus side of the source of energy H].

A potentiometer l1 may be placed in shunt with the crystal to providesuitable means for obtaining variable output voltage.

The output may be taken from the terminals l8 and obviously some othermeans for obtaining a variable output voltage may be employed besidesthe potentiometer as shown. The output may be taken off the crystalelectrodes or terminals Hi, I6.

In Figure 2 the connections and arrangement are substantially the sameas shown in Figure 1, Is, it and ti being the filament, grid and platerespectively of the dynatron tube. In this circuit the radio frequencychoke i2 serves as the plate return to the energy source l0 and may beprovided with the variable tap 22. The usual source of energy 23 isprovided for the filament I9.

It will be observed from the two examples above given that the piezoelectric crystal I5 will cause the system as a whole to oscillate at thenatural frequency of the crystal, the only requirement being that thevalue of the negative resistance of the tube or other device be lowenough to enable it to supply the losses in the crystal, i. e. capableof returning to the crystal,

each half cycle, as much energy as the crystal expended during theprevious half cycle, which condition is necessary for sustainedoscillations.

As the operation of the various component parts of the two circuitsshown herein by way of example and the operation of the piezo electriccrystal are well understood by those skilled in the art a detaileddescription is not necessary. For the operation of other negativeresistance devices other than the dynatron and are herein shown anddescribed reference may be had to the pending application hereinbeforementioned and although the invention has been disclosed in connectionwith the specific details of preferred embodiments thereof it must beunderstood that such details are not intended to be limitative of theinvention except insofar as set forth in the accompanying claims.

What is claimed is:

1. In combination, an output circuit including a source of energy, anegative resistance device including a radio frequency choke, a piezoelectric crystal means for energizing said device from said source ofenergy, a, condenser in series with said crystal, said condenser andcrystal series being connected in shunt with said negative resistancedevice with the condenser positioned between said crystal and a positiveelectrode in said device, and a potentiometer in parallel with saidcrystal and output terminals for said combination connected to saidpotentiometer.

2. In combination, an output circuit including a negative resistancedevice comprising a filament, a grid, a plate and a radio frequencychoke, a source of energy connected to said grid and said filament, saidradio frequency choke connecting said plate to said source of energy, a

condenser connected to said plate, a piezo elec-.?

tric crystal in series with said condenser and connected to the negativeside 'of said source of energy, and a voltage divider in multiplewithsaid crystal and connecting with the output terminals of saidcombination for controlling the potential output thereof.

3. In combination, an output circuit including a negative resistancedevice comprising a filament, a grid, 9. plate, a piezo electric crystaland a radio frequency choke, a source of energy connected to said gridand said filament, a connection through said choke from one pole of saidsource of energy to said plate and a connection between said piezoelectric crystal and said source of energy, a condenser, said piezoelectric crystal being in series with said condenser connected to saidplate and to the negative side ofzsaid source of energy, the condenserbeing positioned between said crystal and the plate, and a potentiometershunted against said crystal, the negative resistance of said devicebeing of a valuelow enough tosupply energy to said crystal duringany=half cycle equal to the energy expended in the crystal during theprevious half cycle.

EARL L. KOCH.

